Asymmetric patterned magnetic memory

ABSTRACT

This invention provides an asymmetrically patterned magnetic memory storage device. In a particular embodiment at least one magnetic memory cell is provided. Each magnetic memory cell provides at least one ferromagnetic data layer of a first size, the data layer characterized by an alterable orientation of magnetization, an intermediate layer in contact with the data layer and at least one ferromagnetic reference layer of a second size, the reference layer characterized by a reference magnetic field. The reference layer is in contact with the intermediate layer, opposite from and asymmetric to the data layer. The magnetic memory cell is characterized as having only one-end involvement. More specifically, the asymmetric alignment provides that only one set of magnetic poles are in substantial vertical alignment, and as such subject to the strong influence of one another.

FIELD OF THE INVENTION

This invention relates generally to magnetic memory devices and inparticular to ultra-high density asymmetrical magnetic random accessmemory (commonly referred to as “MRAM”).

BACKGROUND OF THE INVENTION

Today's computer systems are becoming increasingly sophisticated,permitting users to perform an ever greater variety of computing tasksat faster and faster rates. The size of the memory and the speed atwhich it can be accessed bear heavily upon the overall speed of thecomputer system.

Generally, the principle underlying the storage of data in a magneticmedia (main or mass storage) is the ability to change, and/or reverse,the relative orientation of the magnetization of a storage data bit(i.e. the logic state of a “0” or a “1”). The coercivity of a materialis the level of demagnetizing force that must be applied to a magneticparticle to reduce and/or reverse the magnetization of the particle.Generally speaking, the smaller the magnetic particle the higher it'scoercivity.

A prior art magnetic memory cell may be a tunneling magneto-resistancememory cell (TMR), a giant magneto-resistance memory cell (GMR), or acolossal magneto-resistance memory cell (CMR). These types of magneticmemory are commonly referred to as magnetic tunnel junction memory(MTJ). As shown in prior art FIGS. 1A and 1B a magnetic tunnel junctionmemory 100 generally includes a data layer 101 (also called a storagelayer or bit layer), a reference layer 103, and an intermediate layer105 between the data layer 101 and the reference layer 103. The datalayer 101, the reference layer 103, and the intermediate layer 105 canbe made from one or more layers of material.

The data layer 101 is usually a layer of magnetic material that stores abit of data as an orientation of magnetization M2 that may be altered inresponse to the application of an external magnetic field or fields.More specifically, the orientation of magnetization M2 of the data layer101 representing the logic state can be rotated (switched) from a firstorientation representing a logic state of “0” to a second orientation,representing a logic state of “1”, and/or vice versa.

The reference layer 103 is usually a layer of magnetic material in whichan orientation of magnetization M1 is “pinned”, as in fixed, in apredetermined direction. Often several layers of magnetic material arerequired and function as one to effectuate a stable pinned referencelayer 103. The direction is predetermined and established bymicroelectronic processing steps employed in the fabrication of themagnetic memory cell.

The data layer 101 and reference layer 103 may be thought of as stackedbar magnets, each long on the X axis 107 and short on the Y axis 109.The magnetization of each layer has a strong preference to align alongthe easy axis, generally the long X axis 107. The short Y axis 109 isthe hard axis. As with traditional bar magnets, the data layer andreference layer each have magnetic poles, one at either end of the easyaxis.

The lines of magnetic force that surround a bar magnet arethree-dimensional and flow from the North to the South pole. FIG. 2A isa simplified side view illustration of a typical bar magnet 200, it'smagnetic orientation M and the surrounding magnetic field also referredto as lines of force (represented by arrows 201). As is shown in FIGS.2B and 2C, generally, like poles repel and unlike poles attract. Whenopposite poles of two bar magnets (203 and 203′) are brought together,the lines of force 201 join up and pull the magnets together as in FIG.2B. When like poles of two bar magnets (205 and 205′) are broughttogether, the lines of force 201 push away from each other and themagnets repel each other as in FIG. 2C.

These forces are most pronounced at either pole. As a result when twobar magnets of substantially equal length are evenly stacked lengthwise,both poles either simultaneously attract or simultaneously repel as theyare directly proximity to one another.

Typically, the logic state (a “0” or a “1”) of a magnetic memory celldepends on the relative orientations of magnetization in the data layer101 and the reference layer 103. For example, when an electricalpotential bias is applied across the data layer 101 and the referencelayer 103 in a MTJ 100, electrons migrate between the data layer 101 andthe reference layer 103 through the intermediate layer 105. Theintermediate layer 105 is typically a thin dielectric layer commonlyreferred to as a tunnel barrier layer. The phenomena that cause themigration of electrons through the barrier layer may be referred to asquantum mechanical tunneling or spin tunneling.

Continuing with the model of an elemental bar magnets, the magnetizationof the data layer 101 is free to rotate, but with a strong preference toalign in either direction along the easy axis 107 of the data layer 101.The reference layer 103 likewise is aligned along the easy axis 107 ofthe reference layer 103, but is pinned in a fixed alignment. The logicstate may be determined by measuring the resistance of the memory cell.For example, if the overall orientation of the magnetization in the datalayer 101 is parallel to the pinned orientation of magnetization in thereference layer 103 the magnetic memory cell will be in a state of lowresistance. If the overall orientation of the magnetization in the datalayer 101 is anti-parallel (opposite) to the pinned orientation ofmagnetization in the reference layer 103 the magnetic memory cell willbe in a state of high resistance.

As the data layer 101 and reference layer 103 are substantially equal inlength, and as the physical ends of the data layer 101 and referencelayer 103 are symmetrically aligned, the poles of each layer are alsoproximate to one another. When the magnetic fields M1 and M2 areanti-parallel, as in FIG. 1A, there exists a strong magnetic attractionbetween both ends as illustrated by joined field lines 111 and 113. Whenthe magnetic fields M1 and M2 are parallel, as in FIG. 1B, the magneticfields emanating from the poles repel one another, as illustrated byfield lines 115 and 117. As the poles are pre-disposed to attract, thereis a strong desire for both poles of the data layer 101 to rotate awayfrom their matching pole in the reference layer 103, as represented byarrows 119. This symmetric set of forces operating upon both ends of thedata layer 101 and reference layer 103 at substantially the same timemay be described simplistically as “two-end involvement.”

Storing a binary one or zero in the data layer 101 may require theorientation of the data layer 101 to be rotated, an event that may forcethe like poles to align, a condition they will fight, or permit oppositepoles to align, a condition they desire. In either case, both poles ofthe data layer 101 and the reference layer 103 are involved and must becoerced to accept the new orientation. While the attraction between thepoles reduces the required field to shift the orientation intoanti-parallel, the repulsion at both ends requires a greater field toshift the orientation into parallel.

In an ideal setting the orientation of the alterable magnetic field inthe data layer 101 would be either parallel or anti-parallel withrespect to the field of the reference layer 103. As the data layer 101and the reference layer 103 are generally both made from ferromagneticmaterials and are positioned in close permanent proximity to each other,the generally stronger reference layer 103 may affect the orientation ofthe data layer 101. More specifically, the magnetization of thereference layer 103 may generate a demagnetization field that extendsfrom the reference layer 103 into the data layer 101.

The result of this demagnetization field from the reference layer 103 isan offset in the coercive switching field. This offset can result inasymmetry in the switching characteristics of the bit: the amount ofswitching field needed to switch the bit from parallel to anti-parallelstate is different from the switching field needed to switch the bitfrom anti-parallel state to parallel state. To have reliable switchingcharacteristics and to simplify the read/write circuitry, it isdesirable to have this offset reduced to as near zero as possible.

The magneto-resistance AR/R may be described as akin to asignal-to-noise ratio S/N. A higher S/N results in a stronger signalthat can be sensed to determine the state of the bit in the data layer101. Thus, at least one disadvantage of a tunnel junction memory cellhaving a pinned reference layer 103 in close and fixed proximity to thedata layer 101 is a potential reduction in the magneto-resistance AR/Rresulting from the angular displacement.

To pin the reference layer 103 during manufacturing, the reference layer103 must be heated to an elevated temperature in an annealing step. Theannealing step typically takes time, perhaps an hour or more. As thereference layer 103 is but one part of the memory being produced, theentire memory must be subject to temperatures ranging from about 200 to300 degrees centigrade while under the influence of a constant andfocused magnetic field. Such manufacturing stresses may permit thereference layer 103 to become un-pinned and lose it's set orientation ifthe memory is later subjected to high temperatures. In addition, thecharacteristics of the data layer 101 may be unknowingly affected byheat during some manufacturing processes.

To facilitate establishing a pinned reference layer 103 it is notuncommon for the reference layer 103 to include multiple layers ofmaterial. While utilizing multiple layers may help ensure that thereference layer 103 remains pinned, it also raises the complexity ofmanufacturing each and every memory cell present in the magnetic memory.

Main memory devices such as MRAM often employ tunnel junction magneticmemory cells positioned at the transverse intersections of electricallyconductive rows and columns. Such an arrangement is known as across-point memory array.

In a typical cross-point memory array, while any given row (row A, B, C. . . ) may cross every column (column 1, 2, 3 . . . ), and visa-versa,the traditional principles of column and row arrays dictate that anygiven row will only cross any given column once. Therefore, by-accessinga particular row (B) and a particular column (3), any one memory cellpositioned at their intersection (B,3) can be isolated from any othermemory cell in the array. Such individual indexing is not withoutcomplexities.

As between the two fundamental operations that may be performed on astorage bit (a “write” or a “read”), the write operation is generallymore complex. With respect to traditional cross-point memory arrays,while the magnetic field of the data layer 101 of a desired cell may bealtered, it is desirable not to adversely affect or alter the datalayers 101 of neighboring cells. Write operations generally requiregreater electrical current and magnetic fields, requiring more robustcharacteristics in the power supply, row and column conductors andappropriate buffering space. Therefore, design and manufacturing issuesare generally focused upon the requirements imposed by the writeoperation.

With respect to magnetic memory components, it is well known that assize decreases coercivity increases. A large coercivity is generallyundesirable, as it requires a greater magnetic field to be switched,which in turn requires a greater power source and potentially largerswitching transistors. Providing large power sources and large switchingtransistors is generally at odds with the focus of nanotechnology toreduce the necessary size of components. In addition, to mitigate thepotential of inadvertently switching a neighboring memory cell,nanometer scaled memory cells are generally more widely spaced relativeto their overall size than are non-nanometer sized memory cells.Moreover, as the size of the magnetic memory decreases, the unused spacebetween individual memory cells tends to increase.

These issues and current design of the magnetic memory cells also carryover into the design and use of magnetic field sensors such as thosecommonly used in hard drive read cells and read heads. In suchimplementation, the data layer 101 is termed a sense layer and isoriented by the magnetic field emanating from a storage bit proximate tothe read head. As two-end involvement is present, weakend or degradeddata storage bits on the hard drive may not have a sufficient field toproperly orient the sense layer.

Hence, in a typical MRAM array a significant amount of overall space maybe used simply to provide a physical buffer between the cells. Absentthis buffering space, or otherwise reducing it's ratio, a greater volumeof storage in the same physical space could be obtained.

Hence, there is a need for an ultra-high density thermally assistedmemory array which overcomes one or more of the drawbacks identifiedabove. The present invention satisfies one or more of these needs.

SUMMARY

This invention provides an asymmetrically patterned magnetic memorystorage device.

In particular, and by way of example only, according to an embodiment ofthe present invention, this invention provides an asymmetricallypatterned magnetic device including: at least one ferromagnetic datalayer of a first size, the data layer characterized by an alterableorientation of magnetization; an intermediate layer in contact with thedata layer; and at least one ferromagnetic reference layer of a secondsize, the reference layer characterized by a reference magnetic field,the reference layer in contact with the intermediate layer, oppositefrom and asymmetric to the data layer.

Moreover, according to an embodiment thereof, the invention may providean asymmetrically patterned magnetic memory storage device including: atleast one magnetic memory cell, each cell characterized by: at least oneferromagnetic data layer of a first size, the data layer characterizedby an alterable orientation of magnetization; an intermediate layer incontact with the data layer; and at least one ferromagnetic referencelayer of a second size, the reference layer characterized by a referencemagnetic field, the reference layer in contact with the intermediatelayer, opposite from and asymmetric to the data layer.

Further, according to an embodiment thereof, the invention may providean asymmetrically patterned magnetic memory storage device including: atleast one magnetic memory cell, each cell characterized by: at least oneferromagnetic data layer of a first size having a first end, a secondend and a length along a longitudinal axis therebetween, and furthercharacterized by an alterable orientation of magnetization along thelongitudinal axis, the alterable magnetization having a North pole and aSouth pole aligning to each end of the data layer; an intermediate layerin contact with the data layer; and a ferromagnetic reference layer of asecond size in contact with the intermediate layer, opposite from andasymmetric to the data layer, the reference layer having a first end, asecond end, and a length along a longitudinal axis therebetween, andfurther characterized by a reference magnetic field along thelongitudinal axis, the reference magnetic field having a North pole anda South pole aligning to each end of the reference layer.

In yet another embodiment, the invention may provide an asymmetricallypatterned magnetic memory storage device including: a plurality ofparallel electrically conductive rows; a plurality of parallelelectrically conductive columns transverse to the rows, the columns androws thereby forming a cross point array with a plurality ofintersections; a plurality of magnetic memory cells, each memory celllocated at an intersection between a row and column, each cellcharacterized by: at least one ferromagnetic data layer of a first sizehaving a first end, a second end and a length along a longitudinal axistherebetween, and further characterized by an alterable orientation ofmagnetization along the longitudinal axis, the alterable magnetizationhaving a North pole and a South pole aligning to each end of the datalayer; an intermediate layer in contact with the data layer, and aferromagnetic reference layer of a second size in contact with theintermediate layer, opposite from and asymmetric to the data layer, thereference layer having a first end, a second end, and a length along alongitudinal axis therebetween, and further characterized by a referencemagnetic field along the longitudinal axis, the reference magnetic fieldhaving a North pole and a South pole aligning to each end of thereference layer.

In still another embodiment, the invention may provide a computer systemincluding: a main board; at least one central processing unit (CPU)coupled to the main board; and at least one memory store joined to theCPU by the main board, the memory store having at least one memory cell,each memory cell including; at least one ferromagnetic data layer of afirst size having a first end, a second end and a length along alongitudinal axis therebetween, and further characterized by analterable orientation of magnetization along the longitudinal axis; anintermediate layer in contact with the data layer; and a ferromagneticreference layer of a second size in contact with the intermediate layer,opposite from and asymmetric to the data layer, the reference layerhaving a first end, a second end, and a length along a longitudinal axistherebetween, and further characterized by a reference magnetic fieldalong orientation of magnetization along the longitudinal axis.

These and other objects, features and advantages of the preferred methodand apparatus will become apparent from the following detaileddescription, taken in conjunction with the accompanying drawings whichillustrate, by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B show perspective views of a prior art magnetic memory cellhaving symmetric layers with anti-parallel and parallel magnetic fields;

FIGS. 2A-2C conceptually illustrate the magnetic fields surrounding barmagnets;

FIG. 3A is a plain view of an asymmetrically patterned magnetic memoryaccording to a preferred embodiment of the present invention;

FIG. 3B is a perspective view of the asymmetrically patterned memorycell of FIG. 3A;

FIG. 3C is an alterative embodiment of an asymmetrically patternedmagnetic memory cell of FIG. 3A;

FIG. 4A is a plain view of anti-parallel magnetic fields in theasymmetrically patterned memory of FIG. 3A;

FIG. 4B is a plain view of parallel magnetic fields in theasymmetrically patterned memory of FIG. 3A;

FIG. 4C is a perspective view of anti-parallel magnetic fields in theasymmetrically patterned memory cell of FIG. 3A;

FIG. 5 is a perspective view illustrating a portion of a cross-pointmemory array consisting of the asymmetrically patterned memory of FIG.3A.

DETAILED DESCRIPTION

Before proceeding with the detailed description, it is to be appreciatedthat the present invention is not limited to use or application with aspecific type of magnetic memory. Thus, although the present inventionis, for the convenience of explanation, depicted and described withrespect to typical exemplary embodiments, it will be appreciated thatthis invention may be applied with other types of magnetic memory.

Referring now to the drawings, and more particularly to FIG. 3A, thereis shown a portion of an asymmetrically patterned magnetic memory 300comprising at least one magnetic tunnel junction memory cell 302 (MTJ),according to an embodiment of the present invention. More specificallyMTJ 302 has at least one ferromagnetic data layer 304 of a first size,an intermediate layer 306 in contact with the data layer 304, and aferromagnetic reference layer 308 of a second size with orientation ofmagnetization M1. To achieve a magnetic memory storage device such asMRAM, the MTJ 302 may be placed in electrical contact with anelectrically conductive row 310 transverse to an electrically conductivecolumn 312. FIG. 5 illustrates a portion of such a cross point array asmay be employed in an MRAM configuration.

With respect to FIG. 3A, the ferromagnetic data layer 304 permits thestoring of a bit of data as an alterable orientation of magnetizationM2. The intermediate layer 306 has opposing sides such that the datalayer 304 in contact with one side is in asymmetrical vertical alignmentwith, and substantially uniformly spaced from, the reference layer 308,in contact with the second side of the intermediate layer 306.

The data layer 304 of a first size has a first end 314 and a second end316 and a length 318 along a longitudinal axis 320 therebetween. Thealterable orientation of magnetization M2 is substantially parallel tolongitudinal axis 320, also known as the easy axis. More specifically,in at least one embodiment the magnetic field M2 is substantiallysymmetric about the longitudinal axis 320 of the data layer 304. Inaddition, in at least one embodiment, the data layer 304 is asubstantially planar parallelogram with right angles.

The field of M2 has a positive pole (also referred to as a North pole322) and a negative pole (also referred to as a South pole 324). TheNorth pole 322 and South pole 324 are opposite from one another. Whenthe North pole 322 is aligned to the second end 316 the South pole 324is aligned to the first end 314, and vis-a-versa when M2 is reversed.

The reference layer 308 of a second size has a first end 350 and asecond end 352 and a length 354 along a longitudinal axis 356therebetween. The reference field of magnetization M1 is substantiallyparallel to the length 354, also know as the easy axis. Morespecifically, in at least one embodiment the magnetic field M1 issubstantially symmetric about the longitudinal axis 356 of the referencelayer 308. In addition, in at least one embodiment, the reference layer308 is a substantially planar parallelogram with right angles.

The field of M1 has a positive pole (also referred to as a North pole358) and a negative pole (also referred to as a South pole 360). TheNorth pole 358 and South pole 360 are opposite from one another. Whenthe North pole 358 is aligned to the first end 350 the South pole 360 isaligned to the second end 352. This alignment is reversed if thereference field M1 is reversed.

As shown, more completely in the perspective view of FIG. 3B, the datalayer 304 is smaller than the reference layer 308. Although theillustration depicts a smaller size due to a difference in length (thelength 318 of the data layer 304 being shorter than the length 354 ofthe reference layer 308), under appropriate circumstances the otherdimensions of width and/or height may be smaller as well, see FIG. 3C.As the data layer 304 is smaller in length 318, one and only one pole ofthe data layer 304 and one and only one pole of the reference layer 308(a set of poles) may be substantially proximate to one another as thedata layer 304 and reference layer 308 are asymmetrically stacked. Inaddition, the first end 314 of the data layer 304 is substantiallyvertically aligned with the first end 350 of the reference layer 308.More specifically, in at least one embodiment, the alignment of thefirst end 314 of the data layer 304 is flush with the first end 350 ofthe reference layer 308. In an alternative embodiment as shown in FIG.3C, the first end 314 of the data layer 304 is proximate to, but notflush with the first end 350 of the reference layer 308.

The advantageous result of the asymmetric alignment is conceptuallyillustrated in FIGS. 4A through 4C. As shown, the asymmetric alignmentachieves a MTJ 302 wherein only one pole of the data layer 304 and onepole of the reference layer 308 are in substantially vertical proximatealignment. As such, these vertically proximate, substantially alignedpoles substantially influence one another, while the non-verticallyaligned poles do not substantially influence one another. Thisconfiguration within the MTJ 302 may be described simplistically as“one-end involvement.”

In the instance case shown in FIG. 4A, M2 and M1 are anti-parallel. Inthis configuration, the South pole 324 of the data layer 304 is alignedto the first end 314 of the data layer 304. The South pole 324 istherefore substantially aligned and proximate to the North pole 358 ofthe reference layer 308. A strong attractive magnetic force asrepresented by arrows 400 exists between the first ends (314 and 350)the data layer 304 and the reference layer 308. As the second ends (316and 352) are not substantially aligned, relative to the first ends (314and 350) the attractive force, represented by arrows 402, is minimal.

In the instance case shown in FIG. 4B, M2 and M1 are parallel. In thisconfiguration the North pole 322 of the data layer 304 is aligned to thefirst end 314 of the data layer 304. The North pole 322 is thereforesubstantially aligned and proximate to the North pole 358 of thereference layer 308. A strong repelling magnetic force as represented byarrows 404 exists between the first ends (314 and 350) the data layer304 and the reference layer 308. As the second ends (316 and 352) arenot substantially aligned, relative to the first ends (314 and 350) therepelling force, represented by arrows 406, is minimal. As shown in theperspective view of FIG. 4C, advantageously over the prior art, thealigned North pole 322 of the data layer 304 exhibits a strong repulsiveforce and a desire to swing out of alignment (represented by arrow 408),whereas the South pole 324 of the data layer 304 remains respectivelypassive.

To perform a write operation upon the data layer 304 of MTJ 302, amagnetic field is applied sufficient to overcome the coercitivity of thedata layer 304. Whereas in the prior art the applied magnetic field alsowas required to content with two sets of magnetic poles desiring orresisting the reorientation of M2, under the asymmetric patterning asshown in FIGS. 4A-4C, the write field need only be sufficient toovercome the coercitivity of M2 in the data layer 304 and align one setof poles. More specifically, where a write operation creates a parallelalignment between M1 and M2, a magnetic field is applied to overcome thecoercitivity of the data layer 304 and align the data layer North pole322 at the data layer first end 314 with the reference layer North pole358 at the reference layer first end 350. In an alternative embodiment,where a write operation creates a parallel alignment between M1 and M2,a magnetic field is applied to overcome the coercitivity of the datalayer 304 and align the data layer South pole 324 at the data layerfirst end 314 with the reference layer South pole 360 at the referencelayer first end 350.

The one-end involvement of the asymmetric alignment of the data layer304 and reference layer 308 permits different thresholds in the writemagnetic field strength required to shift M2 from anti-parallel toparallel and from parallel to anti-parallel. Such difference inthresholds permits the MTJ 302 to advantageously operate as a multiplestate cell.

The ability of the asymmetrically patterned magnetic memory 300 to storedata is exemplified in FIG. 5. The write magnetic field may be achievedby passing an externally supplied write current I_(WR) of apredetermined magnitude and direction through conductor row 310resulting in the generation of a magnetic field (represented by curvedarrows 500). In addition, an externally supplied write current I_(WC) ofa predetermined magnitude and direction is supplied through column 312resulting in the generation of a magnetic field (represented by curvedarrows 502).

As shown, the write current I_(WR) of the row 310 is flowing into thepage, indicated by the “+” symbol, such that the magnetic field 500 hasa vector in the clockwise direction in accordance with the right-handrule. The write current I_(WC) of the column 312 is flowing along thepage such that the magnetic field 502 of the column 312 cooperativelyinteracts with the magnetic field 500 of the row 310. The magneticfields 500 and 502 are not sufficient, individually to overcome thecoercivity of the data layer 304 of a MTJ 302 not located at the crosspoint intersection of the row 310 and column 312.

The reference layer 308 may be a pinned or soft reference layer. In atleast one embodiment the reference layer 308 is a soft reference layer,so named because the direction of orientation of magnetization M1 can bedynamically set to a known direction. Such dynamic setting may beachieved by magnetic fields provided by an externally supplied currentflowing through the row 310 and column 312 intersecting at MTJ 302. Inthis case, the current magnitude applied to the row 310 and the column312 to set the magnetization M1 of the soft reference layer 308 to aknown direction is relatively small. This current will not alter themagnetization state M2 of the data layer 304 or other unselected memorycells.

Generally, this event occurs during a read cycle when the magnetizationM1 of the reference layer 308 is set to a known direction and thencompared with the direction of M2 of the data layer 304 to determine the“0” or “1” state of the memory bit cell. It is termed “soft” because itgenerally comprises materials that are magnetically soft and are not ofthe usual hard-pinned materials used for more traditional pinnedreference layers. When utilizing a soft reference layer, a convention isgenerally adopted as to which way M1 will be oriented.

The use of a soft reference layer may have several advantageous benefitsin the MTJ 302. As a soft reference layer is not substantially fixed inorientation, it may not be necessary to subject the MTJ 302 to hightemperatures during manufacturing as is often required to establish afixed reference layer. In addition, the lack of a substantial andconstant magnetic field in the reference layer reduces the likelihood ofa demagnetization field from the reference layer acting upon the datalayer, thus reducing the offset in the coercive switching field.

The ferromagnetic data layer 304 has a lower coercitivity then thereference layer 308, and may be made from a material that includes, butit not limited to: Nickel Iron (NiFe), Nickel Iron Cobalt (NiFeCo),Cobalt Iron (CoFe), and alloys of such metals. In addition, both thereference layer 308 and the data layer 304 may be formed from multiplelayers of materials. However, for conceptual simplicity and ease ofdiscussion, each layer component is herein discussed as a single layer.

The phenomenon that causes the resistance in the MTJ 302 is wellunderstood in the magnetic memory art and is well understood for TMRmemory cells. GMR and CMR memory cells have similar magnetic behaviorbut their magneto-resistance arises from different physical effects asthe electrical conduction mechanisms are different. For instance, in aTMR-based memory cell, the phenomenon is referred to asquantum-mechanical tunneling or spin-dependent tunneling. In a TMRmemory cell, the intermediate layer 306 is a thin barrier of dielectricmaterial through which electrons quantum mechanically tunnel between thedata layer 304 and the reference layer 308.

In a GMR memory cell, the intermediate layer 306 is a thin spacer layerof non-magnetic but conducting material. Here the conduction is aspin-dependent scattering of electrons passing between the data layer304 and the reference layer 308 though the intermediate layer 306. Ineither case, the resistance between the data layer 304 and the referencelayer 308 will increase or decrease depending on the relativeorientations of the magnetic fields M1 and M2. It is that difference inresistance that is sensed to determine if the data layer 304 is storinga logic state of “0” or a logic state of “1”.

In at least one embodiment, the intermediate layer 306 is a tunnel layermade from an electrically insulating material (a dielectric) thatseparates and electrically isolates the data layer 304 from thereference layer 308. Suitable dielectric materials for the dielectricintermediate layer 306 may include, but are not limited to: SiliconOxide (SiO₂), Magnesium Oxide (MgO), Silicon Nitride (SiN_(x)), AluminumOxide (Al₂O₃), Aluminum Nitride (AlN_(x)), and Tantalum Oxide (TaO_(x)).

In at least one other embodiment, the intermediate layer 306 is a tunnellayer made from a non-magnetic material such as a 3d, a 4d, or a 5dtransition metal listed in the periodic table of the elements. Suitablenon-magnetic materials for a non-magnetic intermediate layer 306 mayinclude, but are not limited to: Copper (Cu), Gold (Au) and Silver (Ag).While the actual thickness of the intermediate layer 306 is dependentupon the materials selected to create the intermediate layer 306 and thetype of tunnel memory cell desired, in general, the intermediate layer306 may have a thickness of about 0.5 nm to about 5.0 nm.

It is understood and appreciated that although the above discussionshave pertained generally to magnetic memory cells 302, the discussionspertaining to the structure carry over to magnetic read devices such asread heads for hard drives, or any other magnetic field read sensor. Insuch a setting the data layer 304 is termed a sense layer and isoriented by a magnetic field emanating from a storage bit, rather thanfrom a field provided by, for example a row 310 and a column 312. Indeedthe one-end involvement of asymmetric patterning advantageously permitsthe sense layer (otherwise known as the data layer 304) to respond tosmaller magnetic fields and/or degraded fields.

Another embodiment may be appreciated to be a computer systemincorporating the asymmetrically patterned magnetic memory 300. Acomputer with a main board, CPU and at lest one memory store comprisedof an embodiment of the asymmetrically patterned magnetic memory 300described above raises the advantages of the improved MTJ's 302 to asystem level.

While the invention has been described with reference to the preferredembodiment, it will be understood by those skilled in the art thatvarious alterations, changes and improvements may be made andequivalents may be substituted for the elements thereof and stepsthereof without departing from the scope of the present invention. Inaddition, many modifications may be made to adapt to a particularsituation or material to the teachings of the invention withoutdeparting from the essential scope thereof. Such alterations, changes,modifications, and improvements, though not expressly described above,are nevertheless intended and implied to be within the scope and spiritof the invention. Therefore, it is intended that the invention not belimited to the particular embodiments disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

I claim:
 1. An asymmetrically patterned magnetic device comprising: atleast one ferromagnetic data layer of a first size, the data layercharacterized by an alterable orientation of magnetization; anintermediate layer in contact with the data layer; and at least oneferromagnetic reference layer of a second size, the reference layercharacterized by a reference magnetic field, the reference layer incontact with the intermediate layer, opposite from and asymmetric to thedata layer.
 2. The asymmetric magnetic device of claim 1, wherein themagnetic device is a magnetic field sensor.
 3. The asymmetric magneticdevice of claim 1, wherein the magnetic device is a magnetic memorycell.
 4. The asymmetric magnetic device of claim 1, wherein the datalayer is further characterized as having a first end, a second end, anda length along a longitudinal axis therebetween, the alterablemagnetization having a North pole and a South pole aligning to each endof the data layer; and the reference layer is characterized as having afirst end, a second end, and a length along a longitudinal axistherebetween, the reference magnetic field having a North pole and aSouth pole aligning to each end of the reference layer, and the lengthof the data layer being different from the length of the referencelayer.
 5. The asymmetric magnetic device of claim 4, wherein theinteraction between the poles of the data layer and the poles of thereference layer may be characterized as one-end involvement.
 6. Anasymmetrically patterned magnetic memory storage device comprising: atleast one magnetic memory cell, each cell characterized by: at least oneferromagnetic data layer of a first size, the data layer characterizedby an alterable orientation of magnetization; an intermediate layer incontact with the data layer; and at least one ferromagnetic referencelayer of a second size, the reference layer characterized by a referencemagnetic field, the reference layer in contact with the intermediatelayer, opposite from and asymmetric to the data layer.
 7. The asymmetricmagnetic memory of claim 6, wherein the data layer is smaller than thereference layer.
 8. The asymmetric magnetic memory of claim 6, whereinthe data layer is further characterized as having a first end, a secondend, and a length along a longitudinal axis therebetween, the alterablemagnetization having a North pole and a South pole aligning to each endof the data layer; and the reference layer is characterized as having afirst end, a second end, and a length along a longitudinal axistherebetween, the reference magnetic field having a North pole and aSouth pole aligning to each end of the reference layer, and the lengthof the data layer being different from the length of the referencelayer.
 9. The asymmetric magnetic memory of claim 8, wherein the firstend of the data layer is substantially vertically aligned with the firstend of the reference layer.
 10. The magnetic memory of claim 9, whereinthe interaction between the poles of the data layer and the poles of thereference layer may be characterized as one-end involvement.
 11. Theasymmetric magnetic memory of claim 9, wherein during a write operationto change the alignment of the data layer magnetic field to parallel thereference layer magnetic field, a magnetic field is applied to overcomethe coercitivity of the data layer, the magnetic field sufficient toalign the data layer North pole at the data layer first end with thereference layer North pole at the reference layer first end.
 12. Theasymmetric magnetic memory of claim 8, wherein the magnetic field of thedata layer is substantially symmetric about the longitudinal axis. 13.The asymmetric magnetic memory of claim 12, wherein the data layer is asubstantially planar parallelogram with right angles.
 14. The asymmetricmagnetic memory of claim 6, further comprising: a plurality of parallelelectrically conductive rows; and a plurality of parallel electricallyconductive columns transverse to the rows, the columns and rows therebyforming a cross point array with a plurality of intersections; whereineach memory cell is located at an intersection between a row and acolumn.
 15. The magnetic memory of claim 6, wherein the reference layeris characterized by a pinned orientation of magnetization.
 16. Theasymmetric magnetic memory of claim 6, wherein the reference layer is asoft reference layer, the layer having a non-pinned orientation ofmagnetization.
 17. The asymmetric magnetic memory of claim 6, whereinthe intermediate layer is a tunnel layer.
 18. An asymmetricallypatterned magnetic memory storage device comprising: at least onemagnetic memory cell, each cell characterized by: at least oneferromagnetic data layer of a first size having a first end, a secondend and a length along a longitudinal axis therebetween, and furthercharacterized by an alterable orientation of magnetization along thelongitudinal axis, the alterable magnetization having a North pole and aSouth pole aligning to each end of the data layer; an intermediate layerin contact with the data layer; and a ferromagnetic reference layer of asecond size in contact with the intermediate layer, opposite from andasymmetric to the data layer, the reference layer having a first end, asecond end, and a length along a longitudinal axis therebetween, andfurther characterized by a reference magnetic field along thelongitudinal axis, the reference magnetic field having a North pole anda South pole aligning to each end of the reference layer.
 19. Theasymmetric magnetic memory of claim 18, wherein the magnetic field ofthe data layer is substantially symmetric about the longitudinal axis.20. The asymmetric magnetic memory of claim 19, wherein the data layeris a substantially planar parallelogram with right angles.
 21. Theasymmetric magnetic memory of claim 18, wherein the data layer issmaller than the reference layer.
 22. The asymmetric magnetic memory ofclaim 18, wherein the interaction between the poles of the data layerand the poles of the reference layer may be characterized as one-endinvolvement.
 23. The asymmetric magnetic memory of claim 21, wherein thefirst end of the data layer is substantially vertically aligned with thefirst end of the reference layer.
 24. The asymmetric magnetic memory ofclaim 22, wherein during a write operation to change the alignment ofthe data layer magnetic field to parallel the reference layer magneticfield, a magnetic field is applied to overcome the coercitivity of thedata layer, the magnetic field sufficient to align the data layer Northpole at the data layer first end with the reference layer North pole atthe reference layer first end.
 25. The asymmetric magnetic memory ofclaim 19, wherein the first end of the data layer is flush with thefirst end of the reference layer.
 26. The asymmetric magnetic memory ofclaim 19, wherein the first end of the data layer is proximate to, butnot flush with the first end of the reference layer.
 27. The asymmetricmagnetic memory of claim 18, further comprising: a plurality of parallelelectrically conductive rows; and a plurality of parallel electricallyconductive columns transverse to the rows, the columns and rows therebyforming a cross point array with a plurality of intersections; whereineach memory cell is located at an intersection between a row and acolumn.
 28. The asymmetric magnetic memory of claim 18, wherein thereference layer is characterized by a pinned orientation ofmagnetization.
 29. The asymmetric magnetic memory of claim 18, whereinthe reference layer is a soft reference layer, the layer having anon-pinned orientation of magnetization.
 30. The asymmetric magneticmemory of claim 18, wherein the intermediate layer is a tunnel layer.31. The asymmetric magnetic memory of claim 30, wherein the tunnel layeris a dielectric material.
 32. An asymmetrically patterned magneticmemory storage device comprising: a plurality of parallel electricallyconductive rows; a plurality of parallel electrically conductive columnstransverse to the rows, the columns and rows thereby forming a crosspoint array with a plurality of intersections; a plurality of magneticmemory cells, each memory cell located at an intersection between a rowand column, each cell characterized by: at least one ferromagnetic datalayer of a first size having a first end, a second end and a lengthalong a longitudinal axis therebetween, and further characterized by analterable orientation of magnetization along the longitudinal axis, thealterable magnetization having a North pole and a South pole aligning toeach end of the data layer; an intermediate layer in contact with thedata layer; and a ferromagnetic reference layer of a second size incontact with the intermediate layer, opposite from and asymmetric to thedata layer, the reference layer having a first end, a second end, and alength along a longitudinal axis therebetween, and further characterizedby a reference magnetic field along the longitudinal axis, the referencemagnetic field having a North pole and a South pole aligning to each endof the reference layer.
 33. The asymmetric magnetic memory of claim 32,wherein the interaction between the poles of the data layer and thepoles of the reference layer may be characterized as one-endinvolvement.
 34. The asymmetric magnetic memory of claim 32, wherein themagnetic field of the data layer is substantially symmetric about thelongitudinal axis.
 35. The asymmetric magnetic memory of claim 33,wherein the data layer is a substantially planar parallelogram withright angles.
 36. The asymmetric magnetic memory of claim 32, whereinthe data layer is smaller than the reference layer.
 37. The asymmetricmagnetic memory of claim 36, wherein the first end of the data layer issubstantially vertically aligned with the first end of the referencelayer.